Since this thread has a lot of mention on RTV rubbers, I thought it appropriate to continue with posting this SCUBA mould cast at my Home Foundry.
The picture below was a prop which I used in my ebay ads when listing this item for sale. The mould sold consistently at $19.99 having less than two pounds of aluminium to manufacture. The lead weight you see in the picture was actually cast using RTV then painted silver to have the appearance of lead.
When your going to pour lead into the mould it is best to coat the inside with a coating of soot, this makes removal of the cooled lead weight much easier.
The original mould used as a pattern was also a purchased item, to prepare it as a pattern just did some light sanding to remove imperfections left over from the original caster. By making the pattern smoother than received also made it easier to remove from the sand before casting.
Take close look at the SCUBA mould, looking down into the mould you will see that the sides all have a slight tapper. This tapper is called a relief for sand casting or permanent mould you need 3% to enable easy removal of the pattern.
If your using the lost wax method or lost foam you can produce castings with negative relief such as an aluminium cylinder head or engine block with a water jacket incorporated into the casting..
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